1. Field of the Invention
The present invention relates to a cage that receives a pluggable optical transceiver and an assembly of the cage with the transceiver.
2. Related Prior Art
The pluggable optical transceiver generally provides a light-emitting device and a light-receiving device to communicate optically with optical fibers. The light-emitting device and the light-receiving device are installed in an optical receptacle, while, an electronic circuit electrically connected with those optical devices are installed in the body portion. The pluggable transceiver is to be repeatedly set within a cage made of metal and communicates with the host system that mounts the cage by mating the electrical plug provided in the rear end of the optical transceiver with the electrical connected implemented with the deep end of the cage.
The housing of the transceiver is preferably conductive because, when it is set within the metal cage, the electrically conductive housing accompanied with the metal cage may reduce the EMI radiation from the host system by securely grounding the housing and the cage. A Japanese Patent Application published as JP-2007-233261A has disclosed a type of the grounding architecture where an elastic finger, a ground finger, provided in the metal cover of the transceiver comes in contact with the inner surface of the cage pushed by the optical connecter inserted within the optical recepticle of the tansceiver, while, when the receptacle is free from the optical connector, the elastic finger becomes apart from the cage to facilitate the extraction of the transceiver from the cage.
The U.S. Pat. No. 6,368,153, has disclosed another type of the cage finger, in which the cage provides two types of fingers, one of which protrudes from the peripheral walls outwardly to come in contact with the front panel, while, the other type of the finger protrudes inwardly to come in contact with the transceiver. The cage provides these two types of fingers in plural to secure the plurality of ground path to the host system and to the transceiver.
FIG. 5 illustrates a detail of the cage disclosed in the U.S. Pat. No. 6,368,153. The cage provides a plurality of fingers 9 in the peripheral walls, 6a to 6d, in the front end portion. These fingers 9 are, for instance, divided into two portions, one of which is bent outwardly 9a, while, the other of which is bend inwardly 9b. The former finger 9a comes in contact with the front panel of the host system, while, the latter finger 9b comes in contact with the transceiver when the transceiver is set within the cage.
Generally, in order to set the optical transceiver on the host system through the cage by taking the EMI shielding performance into account, it is necessary not only to stabilize the ground by securely connecting the cage with the front panel and with the cage with fingers but to narrow the gap between the front panel and the cage, between the cage and the transceiver, and between the fingers in the cage to be coming in contact with the front panel or with the transceiver.
Receiver optical communication increases the transmission speed thereof and is now going to exceed 10 Gbps. In such high frequencies, the characteristic wavelength becomes shorter such that a gap with a less dimension may leak the EMI radiation. The fingers of the cage that protrudes outwardly or inwardly may partially fill the gap between the front panel and the cage, that between the cage and the housing of the transceiver. However, the finger arrangement such as shown in FIG. 5 where the outward finger and the inward winger are formed in side-by-side leaves some gaps between the fingers, which probably leak the EMI radiation. Thus, it is necessary to fill the gap not only between the cage and the front panel, and between the cage and the transceiver but also the gaps between the fingers, or to narrow the gaps between the fingers as possible.
The present invention is to provide a new arrangement of the cage finger that enables to narrow the gaps between fingers in addition to make the ground contact at a plurality of points.